Singapore Airlines will stop flying the world's two longest nonstop routes—Singapore to Los Angeles and Singapore to Newark—sometime next year. The reason isn't necessarily because the flights aren't profitable, however. Singapore is trading in all five of its A340-500s, the carrier's only planes capable of the long-haul flights, on orders for additional super-jumbo A380s and new super-efficient A350s.

Whether market factors had anything to do with the cancellations is anyone's guess—in an all-business-class layout, the airline had to fill a lot of expensive seats—but the industry generally agrees that high fuel prices have turned the A340 into an uneconomical plane. Other airlines are also dropping that four-engine model in favor of more efficient twins from Airbus and Boeing.

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The nonstop distances from Singapore are 9,535 miles to Newark and 8,770 miles to Los Angeles. After these flights disappear, the longest remaining flights will be Dallas/Ft. Worth to Sydney on Qantas at 8,578 miles, and Atlanta to Johannesburg on Delta at 8,439 miles.

Presumably, had Singapore wanted to keep the nonstops, it could have included a few 777-200LR models in its latest Boeing order. Those planes can fly a bit farther than even the A340-500, but they're still bigger, with more seats to fill.

Overall, super-long-range flying is expensive. Planes have to carry huge amounts of fuel, meaning that the entire trip burns far more fuel than two shorter flights. The 777-200LR could even make the "holy grail" of ultra-long nonstops, London to Sydney at 10,573 miles, but only with a reduced payload on the westbound trip. And the numbers on that possibility don't look good.

In the future, as engines get ever more efficient and aerodynamic tweaks reduce drag, you may see more super-long-range flights. But with today's technology and high fuel prices, you probably won't see any for quite a while.